Radiotransmission of facsimiles



Feb. 10, 1931. J w LABUS 1,792,312

RADI-OTRANSMISSION 0F FACSIMILES Fil'ed March 5, 1930 Flg. 5.

Inventor:

John W Labus,

I-Iis Attor neg.

Patented Feb. 10, 1931 UNITED STATES- PATEN'E OFFICE JOHN w. mnns'for scnnnncranv, mw Yonx, assrenoaro GENERAL nnncrmc commmr, a CORPORATION or NEW Yoax RADIOTRANSMISSION OI FACSIMILES Application filed March 5,

My invention relates to the transmission of' facsimiles. by radio. It has been found in the transmission of facsimiles by. radio, particularly over long distances, that at certain times the received signal shows a ,lag in time thus producing in the case of the trans-- mission of print a roadening of the letters. When conditions have been es ecially unfavorable and when small rint is being transmitted the letters have ecome blurred and illegible. The cause of this phenomena apparently is due to multi ath transmission of the radlo signal arising rom reflections from the Heaviside layer. It has been observed that the first edge of the letters with respect to the direction of scanning is clean cut whereas the blurring occurs at the opposite ed c. It is the object of my invention to provi e an improved method and means whereby such blurring of the received signal may be greatly reduced if not entirely eliminated. My invention will be better understood from the following description taken in connection with the accompanying drawing, and

its scope will be pointed out in the appended' claims.

Referring to the drawing, Flg. 1 1s a c1rcu1t diagram of receiving apparatus involving my invention; Fig. 2 shows by way of example a letter being transmitted; Figs. 3 and 4 are diagrams representing respectlyely blurred black and white signals received without my invention during the scann ng of the letter shown in ig. 2; and Fig. 5 1s a similar diagram representing the black Slgnals received with the use of my invention.

In the drawing forming a part of this application I have purposely omitted any showin of the sending apparatus since this may ta e the form of well known apparatus employed for this purpose with the exception that it includes a duplication of certain parts to the extent that both black signals and white signals are transmitted, the two s1gnals being transmitted on two different channels. For this purpose two carriers may be used or one carrier wave may be beat by two tones, thus shifting the side bands such that they can be received without interference. 50 At the receiver two units will be used which 1930,. Serial No. 433,457.

receive respectively the black and the white signals, the amphfication and detection of the radio signals taking place in the ordinary way. These two units if used in the usual manner, independently of each other, would record the black and white signals in the manner shown by Figs. 3 and 4 respectively during the scanning at the sending station along the line ab of a letter such as shown for example at 1 in Fig. 2. The rectified black signal, shown plotted a ainst time in Fig. 3, is sharp as at 2 at the fii'stedge of the letter but at each last edge trails ofi in the irregular line 3-4 which, as already mentioned above, is due to the radio circuit. On the other hand the rectified white signal, shown plotted against time in Fi 4, trails 01f in the irregular line 5 at the first edge of the letter and is sharp as shown at 6 at the last edge thereof. It will be understood thata facsimile may be transmitted by sendin either black signals or white signals and om the diagrams forming Figs. 3 and 4 it will be seen that whichever signals are used for the transmission a blurring of the letter will occur at one side or the other thereof.

Referring now to Fig. 1, where I have shown in a diagrammatic manner portions of the two receiving sets 7 and 8 constructed and arranged respectively to receive the black and the white signals, each set 7 and 8 includes a three electrode thermionic 'amplifier 9 having a grid 10 and a plate 11, and a translating device 12 such as a glow tube b means of which the signal is recorded. X common plate battery 14 is shown for the two receiver sets 7 and 8. In the grid and plate circuits of the set 7 are the resistances 16 and 17 respectively and similarly in the grid and plate circuits of the set 8 are the resistances 18' and 19 respectively. B means of the conductors 20 the terminals 0 the resistance 19 are connected with the terminals of the resistance 16, the connectionincluding the condenser 22 and in like manner by means of the conductors 23 the terminalsof the resistance 17 are connected With'the terminals of the resistance 18, the connection including the condenser 24.

With no signal being transmitted thegrids of the'two receivers are biased to cut ofi. At the instant that the black signal current (Fig. 3) should stop, that is at the point 3, the white signal is received by the set 8 and an adequate voltage taken across the resistance 19 of the plate circuit of set 8 is applied to the grid circuit of set 7 to cause a cutting oif of the output thereof. This voltage 1n magnitude is about equal to that of the gridvolta e.

m TVithout the condenser 22 the grid of set 7 would remainbiased as long as the white signal was being received by set For continuous operation therefore it is necessary that the inserted bias be taken oif again in orderthat the receiver may be ready for the reception of-the next signal. This result is effected by the condenser 22. At the lnstant the voltage is applied to it, it offers substantially no resistance but builds up a counter E. M. F. thereby restoring the original condition'in the set 7. The result of apply ng this bias to the grid of black'sig'nal rece vm set 7 is shown by Fig. 5 where t e end of eac 25 black signal is seen at 25 to be cut oii sharplly. It may happen that after the signal as been cut off and the bias afterward removed the continued reception of the echo efiect will cause a small hump as shown for exam- 39 ple at 26. This, however, is not serious as theentire lower portion of the slgnal, together with the hump, may be cut off and discarded. In a manner similar to that ust described, the white signal is caused to be cut ofl? at the proper time by voltage applied to the grid of receiver 8 from the plate circuit of receiver 7, the entire system being symmetrical. Both translating devices 12 may be used to make records, the record made by one being a positive and the record made by the other being a negative. If but one record is to be made the device 12 which is not used may have substituted for it a suitable reslstance.

I have chosen the particular embodiment described above as illustrative of my invention and it will be apparent that various modifications may be made without departing from the spirit and scope of my invention, which modifications I aim to cover by.

- the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States, is 1. In the transmission of facsimiles by radio wherein either black signals or white signalstare transmitted to a receiving apparatus, the method which comprlses transmitting concurrently on a difierent wave length the opposite signals to those being transmito ted, .and causing the latter signalssto modify the operation of the receiving apparatus to produce a sharper recorded signal.

2. In the transmission of facsimiles by radio wherein either black signals or white signals are transmitted to a receiving apparatus, the method of reducing the echo effect upon the receipt of the transmitted signals which comprises transmitting concurrently on a difierent wave length the opposite signals to those transmitted and causing the latter signals to eifecta more sharp cutting oif in the operation of the receiving apparatus.

3. Radio facsimile transmission apparatus comprising means for receiving black signals, means for receiving white signals, a trans.- lating' device associated with one of said means for recordingthe signals thereof, and means responsive to the signal received by the other of said receiving means for reducing the echo effect on said first receiving means.

4. Radio facsimile transmission apparatus comprising separate means for receiving respectively black signals and white signals, a

translating device connected to respond to the signals received by one of said receiving means, and means for applying-to said one means a'corrective impulse from the other re ceiving means.

5. Radio facsimile transmission apparatus comprising means adapted to receive either black signals or white signals, said means including a thermionic amplifier having a grid circuit and a plate circuit, a translating device connected with' said plate circuit and means arranged to receive the signal 0 'posite to that received by said first means or applying a biasing potential to said grid circuit.

6'. adio facsimile transmission apparatus comprising a first receiving means con structed to respond to black signals and including a thermionic amplifier having grid and plate circuits and a translating device connected with said plate circuit and a second receiving means constructed to respond to white signals arranged to apply a bias to said grid circuit at the beginning of each white signal.

- 7. Radio facsimile transmission apparatus comprising a first receiving means constrlfifid, to respond to black signals and m clu mg a thermionic amplifier having grid and plate circuits and a translating device connected-with said plate circuit, a second receiving means constructed to respond to white signals arranged to a ply a bias to said grid circuit at the beginning .of each white signal, and means for removing said bias to prepare the black signal receiving means for the reception of the next signal.

8. Radio facsimile transmission apparatus comprising a receiver constructed to respond to black signals, said receiver includin a thermionic amplifier having grid and pita circuits and a translating device connected with the plate circuit,'a'second similar receiver constructed to respond to white signals, and means whereby a biasing potential is applied to the grid circuit of each receiver from the plate circuit of the other receiver.

9. Radio facsimile transmission apparatus com rising a receiver constructed to respond to b ack signals, said receiver includin a thermionic amplifier havin grid and p ate circuits and a translating evice connected with a plate circuit, a second similar receiver constructed to respond to white signals means whereby a biasing potential is applie to the grid circuit of each receiver from the plate circuit of the' other receiver, and means for removing the biasing potential from each grid circuit to-prepare the receiver thereof or the next signal.

In witness whereof I have hereto set my hand this 4th day of March 1930.

Jomi w. LABUS. 

